Historical Changes in Large River Fish Assemblages of the Americas

<em>Abstract.</em>—The Rio das Velhas is a tributary of the Rio São Francisco, one of Brazil’s largest rivers. It is the Rio São Francisco’s second most important tributary in water volume (mean annual discharge of 631 m<sup>3</sup>/s), with a drainage area of 27,867 km<sup>2</sup>, length of 761 km, and mean width of 38 m. Like many other rivers around the world, it became heavily polluted in the 1900s. The Rio das Velhas is the most polluted river of Minas Gerais state because the basin contains approximately 4.5 million people. Unlike other Brazilian rivers, its fish fauna was studied from 1850 to 1856. Fifty-five fish species were recorded; 20 of them were first described at that time, when there were previously no more than 40 known species in the entire São Francisco basin. Recent fish collections, approximately 150 years later, indicate 107 fish species, but some may be locally extinct. There are good prospects of rehabilitating this fauna because of the connectivity of the Rio das Velhas with the São Francisco main stem, its well-preserved tributaries, and increased investments in sewage treatment.

<em>Abstract.</em>—The Rio Grande is the fourth longest river in North America and the 22nd longest in the world. It begins as a cold headwater stream in Colorado, flows through New Mexico and Texas, where it becomes warm and turbid and finally empties into the Gulf of Mexico. The diversity of native fishes is high in the Rio Grande ranging from freshwater salmonids in its upper reaches to coastal forms in the lower reaches. Historically, about 40 primary freshwater species inhabited the waters of the Rio Grande. Like many rivers throughout North America, the native fish fauna of this river has been irrevocably altered. Species once present are now extinct, others are threatened or endangered, and the majority of the remaining native fishes are declining in both range and numbers. Today, 17 of the 40 primary native freshwater fishes have been either extirpated in part or throughout the Rio Grande drainage. This chapter examines the river, its fauna, and its current plight.


<em>Abstract.</em>—The Virgin–Moapa River system supports nine native fish species or subspecies, of which five are endemic. Woundfin <em>Plagopterus argentissimus </em>and Virgin River chub <em>Gila seminuda </em>are endemic to the main-stem Virgin River, whereas cooler and clearer tributaries are home to the Virgin spinedace <em>Lepidomeda mollispinis</em>. Moapa dace <em>Moapa coriacea </em>and Moapa White River springfish <em>Crenichthys baileyi moapae </em>are found in thermal springs that form the Moapa River, and Moapa speckled dace <em>Rhinichthys osculus moapae </em>is generally found below the springs in cooler waters. The agricultural heritage of the Virgin–Moapa River system resulted in numerous diversions that increased as municipal demands rose in recent years. In the early 1900s, trout were introduced into some of the cooler tributary streams, adversely affecting Virgin spinedace and other native species. The creation of Lake Mead in 1935 inundated the lower 80 km of the Virgin River and the lower 8 km of the Moapa River. Shortly thereafter, nonnative fishes invaded upstream from Lake Mead, and these species have continued to proliferate. Growing communities continue to compete for Virgin River water. These anthropogenic changes have reduced distribution and abundance of the native Virgin–Moapa River system fish fauna. The woundfin, Virgin River chub, and Moapa dace are listed as endangered, and the Virgin spinedace has been proposed for listing. In this paper we document how the abundance of these species has declined since the Endangered Species Act of 1973. Currently, there is no strong main-stem refugium for the Virgin River native fishes, tributary refugia continue to be shortened, and the Moapa River native fishes continue to be jeopardized. Recovery efforts for the listed and other native fishes, especially in the Virgin River, have monitored the declines, but have not implemented recovery actions effective in reversing them.


<em>Abstract.</em>—In this paper, we review information regarding the status of the native fishes of the combined Sacramento River and San Joaquin River drainages (hereinafter the “Sacramento–San Joaquin drainage”) and the factors associated with their declines. The Sacramento–San Joaquin drainage is the center of fish evolution in California, giving rise to 17 endemic species of a total native fish fauna of 28 species. Rapid changes in land use and water use beginning with the Gold Rush in the 1850s and continuing to the present have resulted in the extinction, extirpation, and reduction in range and abundance of the native fishes. Multiple factors are associated with the declines of native fishes, including habitat alteration and loss, water storage and diversion, flow alteration, water quality, and invasions of alien species. Although native fishes can be quite tolerant of stressful physical conditions, in some rivers of the drainage the physical habitat has been altered to the extent that it is now more suited for alien species. This interaction of environmental changes and invasions of alien species makes it difficult to predict the benefits of restoration efforts to native fishes. Possible effects of climate change on California’s aquatic habitats add additional complexity to restoration of native fishes. Unless protection and restoration of native fishes is explicitly considered in future water management decisions, declines are likely to continue.


<em>Abstract.</em>—From its headwaters in the Rocky Mountains, the Platte River drains 230,362 km<sup>2</sup> in Colorado, Wyoming, and Nebraska. The Platte River is formed by the confluence of the North Platte and South Platte near the city of North Platte, Nebraska, and receives additional flow from the Loup and Elkhorn rivers that drain the Sand Hills region of Nebraska. Water diversions for mining and irrigation began in the 1840s in Colorado and Wyoming, and irrigation diversions in Nebraska began in the 1850s. Construction of dams for control of river flows commenced on the North Platte River in Wyoming in 1904. Additional dams and diversions in the North Platte, South Platte, and Platte rivers have extensively modified natural flow patterns and caused interruptions of flows. Pollution, from mining, industrial, municipal, and agricultural sources, and introductions of 24 nonnative species have also taken their toll. Fishes of the basin were little studied before changes in land use, pollution, and introduction of exotic species began. The current fish fauna totals approximately 100 species from 20 families. Native species richness declines westward, but some species find refugia in western headwaters streams. Declines in 26 native species has led to their being listing as species of concern by one or more basin states.


<em>Abstract.</em>—The interior Río Nazas basin is located in arid north-central México. It is an interior drainage, subject to dewatering since the early 20th century, and sustains wide fluctuations in runoff. It drains 85,530 km<sup>2</sup> and has a major dam in the middle reaches, producing a highly controlled river, with 100% consumption for agriculture and urban use. Hydrologic gauge reports at Torreón from the Comisión Nacional del Agua indicate a 10-year average runoff of 581.9 million m3 from 1936 to 1945, and only 66.4 million m3 in 1972, the last year of recorded runoff. Its 13 known native fish species are of Rio Grande/Rio Bravo origin. Eleven are endemic to the basin complex (only one absent from the study area), seven species have been listed by the Mexican federal government as threatened or endangered, and three are undescribed. The basin has 13 invasive alien species. An index of biological integrity (IBI), based on historical data, was applied to the current fish assemblage at 10 localities in the lower basin, below El Palmito reservoir. The IBI ranged from 50 to 57 at sites in the northern branch, to 39–61 in the southern branches, and to 0–57 from below their junction to the lower reaches, and averaged 37 or very poor. The overall biotic integrity is very low, especially near reservoirs and in the lower reaches of the river, where human activities consume all available water. The main causes of fish loss from this interesting fish fauna are alien invasive species, habitat disruption, pollution, and dewatering.


2006 ◽  
Vol 4 (4) ◽  
pp. 427-433 ◽  
Author(s):  
Paulo dos Santos Pompeu ◽  
Hugo Pereira Godinho

In the Neotropics, a large proportion of fish communities of large rivers use floodplain as habitats for feeding, reproduction, and refuge. An evaluation was made of the effects of extended dry periods on the species richness, abundance and local extinction of fish species in three marginal lagoons in the middle São Francisco River, southeastern Brazil. The studied lagoons fail to receive river floods during the study period (1994-1996). A gradual reduction in richness and abundance was observed in all lagoons. Migratory fish species had the highest probability to become extinct in the two lagoons that remained with large water volume. Species tolerant to low levels of dissolved oxygen had the lowest probability of local extinction in the lagoon showing an abrupt reduction in water volume. Similar changes to those observed in the current study are likely to occur in the floodplains if dams would be constructed in this segment of the river. Adequate water releases from Três Marias reservoir, located upstream, should be considered as a management tool for producing episodic flooding on the marginal lagoons of the region.


<em>Abstract.</em>—The upper Colorado River basin supports a native ichthyofauna of 14 species or subspecies that have been impacted by poor land-use practices, altered flows, physical habitat fragmentation, competition and predation from nonnative fish species, and degraded water quality. Five taxa are federally endangered, including the large-river species, Colorado pikeminnow <em>Ptychocheilus lucius</em>, humpback chub <em>Gila cypha</em>, bonytail <em>G. elegans</em>, razorback sucker <em>Xyrauchen texanus</em>, and a warm-stream subspecies, Kendall Warm Springs dace <em>Rhinichthys osculus thermalis</em>. Two recovery programs, formed through cooperative agreements among federal, state, tribal, and private agencies and stakeholders, coordinate activities in the upper basin that have helped to resolve water resource issues, implement management actions to minimize or remove threats, and conserve endangered species. A cooperative biological management program among state and federal agencies works to protect the Kendall Warm Springs dace. Conservation agreements have also been established for the other native fish species. Continued public and institutional support for these programs is vital to species recovery and to the balance between long-term species conservation and human demands on the Colorado River system.


<em>Abstract.</em>—The lower Colorado is among the most regulated rivers in the world. It ranks as the fifth largest river in volume in the coterminous United States, but its flow is fully allocated and no longer reaches the sea. Lower basin reservoirs flood nearly one third of the river channel and store 2 years of annual flow. Diverted water irrigates 1.5 million ha of cropland and provides water for industry and domestic use by 22 million people in the southwestern United States and northern Mexico. The native fish community of the lower Colorado River was among the most unique in the world, and the main stem was home to nine freshwater species, all of which were endemic to the basin. Today, five are extirpated, seven are federally endangered, and three are being reintroduced through stocking. Decline of the native fauna is attributed to predation by nonnative fishes and physical habitat degradation. Nearly 80 alien species have been introduced, and more than 20 now are common. These nonnative species thrived in modified habitats, where they largely eliminated the native kinds. As a result, the lower Colorado River has the dubious distinction of being among the few major rivers of the world with an entirely introduced fish fauna.


2021 ◽  
Author(s):  
Nurul F.M. Fadzil ◽  
Zarul H. Hashim ◽  
Amir S. R. M. Sah ◽  
Shahrul A. M. Sah ◽  
Amirul A. A. Aziz ◽  
...  

Abstract Instream barriers such as waterfalls and man-made dams may result in distinct fish assemblages on both sides of the barriers. To determine the influence of these barriers on fish assemblages, a study was conducted in Sungai Enam that have substantial barriers including an 18-m high waterfall with 6.1% slope. Fish were captured using a backpack electrofishing gear together with scoop nets. Thirteen fish species from six families were recorded along this stream, but only Poropuntius smedleyi (Cyprinidae) can be found along the stream and the reach above the waterfall. Studies on a second site, Sungai Kooi, that has a 65m high and 90° slope waterfall, revealed eight fish species from three families, but only P. smedleyi and Devario regina (Cyprinidae) occurred above the waterfall. The number of species in both streams increases from upstream to downstream. A chi-square test revealed that the total number of species among reaches in Sungai Enam differed significantly. Fish species found above the waterfall are known to have no special adaptations to climb or jump over the barriers. Therefore, to explain their existence above the substantial waterfalls especially in Sungai Kooi, we proposed three hypotheses: (1) the world was once flooded and there was no limitation to fish distribution, (2) fish species assemblages were separated by land uplifting, and (3) there are other stream branches enabling fish movement into respective streams. Further studies are required to confirm these hypotheses.


2015 ◽  
Vol 13 (3) ◽  
pp. 579-590 ◽  
Author(s):  
Carolina Rodrigues Bordignon ◽  
Lilian Casatti ◽  
María Angélica Pérez-Mayorga ◽  
Fabrício Barreto Teresa ◽  
Gabriel Lourenço Brejão

The functional structure of communities is commonly measured by the variability in functional traits, which may demonstrate complementarity or redundancy patterns. In this study, we tested the influence of environmental variables on the functional structure of fish assemblages in Amazonian streams within a deforestation gradient. We calculated six ecomorphological traits related to habitat use from each fish species, and used them to calculate the net relatedness index (NRI) and the nearest taxon index (NTI). The set of species that used the habitat differently (complementary or overdispersed assemblages) occurred in sites with a greater proportion of forests. The set of species that used the habitat in a similar way (redundant or clustered assemblages) occurred in sites with a greater proportion of grasses in the stream banks. Therefore, the deforestation of entire watersheds, which has occurred in many Amazonian regions, may be a central factor for the functional homogenization of fish fauna.


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